Oh, mine is large enough," Tom broke in.

"Then it's finished!" cried Ned eagerly, for he was much interested in
his chum's inventions.

"Well, not exactly," Tom said. "But what I was going to tell you was
that all guns are not necessarily large. You can get big results with
small guns and projectiles now, for high-powered explosives come in
small packages. So it isn't altogether a question of carrying a certain
amount of weight. Of course, an aerial warship will have to be big, for
it will have to carry extra machinery to give it extra speed, and it
will have to carry a certain armament, and a large crew will be needed.
So, as I said, it will need to be large. But that problem isn't
worrying me."

"Well, what is it, then?" asked Ned.

"It's the recoil," said Tom, with a gesture of despair.

"The recoil?" questioned Ned, wonderingly.

"Yes, from the guns, you know. I haven't been able to overcome that,
and, until I do, I'm afraid my latest invention will be a failure."

Ned shook his head.

"I'm afraid I can't help you any," he said. "The only thing I know
about recoils is connected with an old shotgun my father used to own.

"I took that once, when he didn't know it," Ned proceeded. "It was
pretty heavily loaded, for the crows had been having fun in our
cornfield, and dad had been shooting at them. This time I thought I'd
take a chance.

"Well, I fired the gun. But it must have had a double charge in it and
been rusted at that. All I know is that after I pulled the trigger I
thought the end of the world had come. I heard a clap of thunder, and
then I went flying over backward into a blackberry patch."

"That was the recoil," said Tom.

"The what?" asked Ned.

"The recoil. The recoil of the gun knocked you over."

"Oh, yes," observed Ned, rubbing his shoulder in a reflective sort of
way. "I always thought it was something like that. But, at the time I
put it down to an explosion, and let it go at that."

"No, it wasn't an explosion, properly speaking," said Tom. "You see,
when powder explodes, in a gun, or otherwise, its force is exerted in
all directions, up, down and every way."

"This went mostly backward--in my direction," said Ned ruefully.

"You only thought so," returned Tom. "Most of the power went out in
front, to force out the shot. Part of it, of course, was exerted on the
barrel of the gun--that was sideways--but the strength of the steel
held it in. And part of the force went backward a